1. Field of the Invention
The present invention relates to a reclining device and to a manufacturing method thereof.
2. Description of the Related Art
As for the seat reclining device for use in a vehicle, there have been known various kinds of devices, one example of which is disclosed in Japanese Patent Unexamined Publication No. H7(1995)-136032.
According to this known seat reclining device, a casing attached to the base plate of a seat cushion and a cap attached to the arm plate of a seat back are rotatably coupled with each other. When it is desired that the casing and the cap are fixed relative to each other, a cam plate mounted on an operating shaft is rotated by a predetermined degree, thereby shifting a locking tooth of the casing toward an internal tooth gear formed on the inner circumferential surface of the cap so as to engage the locking tooth with the internal tooth gear. With this, due to the contact between the cam plate and a cam face formed on the locking tooth, the locking tooth is pressed onto the internal tooth gear.
When it is desired that the casing and the cap are rotated relative to each other, the cam plate is rotated in the opposite direction, thereby moving the locking tooth away from the internal tooth gear so as to disengage the locking tooth from the internal tooth gear.
The cam plate is designed such that two locking teeth located axially opposite to each other can be simultaneously moved by the cam plate. In order to ensure the engagement between each of these locking teeth and the internal tooth gear, clearance has to be provided between the hole of the cam plate and the operating shaft. Due to this clearance, looseness is generated between the cam plate and the operating shaft, causing backlash and noise.
With a view to solving this problem, it has been proposed that the operating lever be provided with a spring. This proposal, however, invites problems in that the number of parts and the number of steps for assembling the device are increased.
Further, according to this known seat reclining device, the magnitude of shift of the locking tooth portion toward the internal tooth gear is very small as compared with the magnitude of shift of the cam face of the cam plate in a circumferential direction. In other words, non-uniformity of the distance between the locking tooth and the internal tooth gear is amplified to a larger non-uniformity in the range of rotation of the cam plate and of the operating shaft. Due to the non-uniformity of all the constituent components, the range of the rotational angle of the operating shaft varies individually. This causes a problem in that the angle of the operating lever coupled to the operating shaft cannot be constant.
Therefore, an object of the present invention is to provide a reclining device which can prevent the generation of abnormal noise and also can minimize the non-uniformityof the range of the rotational angle of the operating shaft, while maintaining the balance of the thrusting force between the cam plate and the locking tooth portion.
A first aspect of the present invention is a reclining device comprising: a casing; a cap rotatably mounted on the casing, having a first gear along the inner circumference thereof; a plurality of second gears for engaging with the first gear, each having a first locking cam face, disposed in axial symmetry with a rotational axis of the casing; a cam comprising a plurality of second locking cam faces for pressing the first locking cam faces to thereby engage the second gear with the first gear, disposed in axial symmetry with a rotational axis of the cam; and a plurality of guiding faces disposed in axial symmetry with a rotational axis of the cam and on a straight line perpendicular to a line that passes through two second locking cam faces located axially opposite each other; and a plurality of guides for guiding the guiding faces, disposed in axial symmetry with a rotational axis of the casing and on a straight line perpendicular to a line passing through two first locking cam faces located axially opposite each other.
A second aspect of the present invention is the reclining device according to the first aspect, wherein each of the guiding faces is formed as a circular arc centered on the rotational axis of the cam, thereby enabling the guiding faces to always be in contact with the guides in the rotation range of the cam.
Since the reclining device is constructed as described above, the movement of the cam is restricted whilst the freedom of rotation is secured, thereby stabilizing the cam. In other words, since the cam is allowed to freely rotate to a position where its pressing force to each of the second gears can be balanced, the tooth of each of second gears can be reliably engaged with the first gear. Accordingly, since it is no longer necessary to provide any play in the fitting between the center hole of the cam and the shaft, the generation of noise due to play can be prevented and, at the same time, the number of parts and the number of steps for assembling the device can be reduced.
A third aspect of the present invention is the reclining device according to the first aspect, further comprising a shaft having a coupling portion for transmitting external torque, wherein the shaft is configured to be press-fitted into a center hole of the cam when the coupling portion is aligned with the casing at a predetermined rotational angle.
A fourth aspect of the present invention is the reclining device according to the third aspect, wherein the shaft is configured to be press-fitted into the center hole of the cam after the second gears engage with the first gear at a predetermined rotational angle.
A fifth aspect of the present invention is the reclining device according to the third aspect, further comprising a seat cushion, a seat back, and a connecting shaft, wherein one of the casing and the cap is disposed on both the right and left sides of the seat cushion, and the other is disposed on both the right and left sides of the seat back, and the connecting shaft connects the respective shafts at both the right and left sides via the respective coupling portions.
Since the reclining device is further constructed as described above, it is possible to press-fit the shaft into the center hole of the cam after finishing the assembly of the casing, the cap, the second gears and the cam.
Further, the rotational angle of the shaft with respect to the casing can be locked. Accordingly, when the operating lever is attached to each of the coupling portions of the shaft, the extending direction of the operating lever can be kept constant.
In a case where the casing is coupled with the seat cushion, the shaft can be kept at a predetermined angle with respect to the seat cushion. In other words, when the operating lever is attached to the shaft, for example, the operating lever can be kept at a predetermined angle with respect to the seat cushion.
A sixth aspect of the present invention is the reclining device according to the fifth aspect, wherein the coupling portions connected to the connecting shaft have play interposed therebetween of predetermined angle in a rotational direction.
A seventh aspect of the present invention is a method of manufacturing the reclining device according to the first aspect, comprising the steps of: a) preparing a casing, a cap, second gears, a cam and a shaft; the cap being rotatably mounted to the casing, having a first gear along its inner circumference; a plurality of the second gears for engaging with the first gear, each having a first locking cam face, disposed in axial symmetry with a rotational axis of the casing; the cam comprising a plurality of second locking cam faces for pressing the first locking cam faces to thereby engage the second gears with the first gear, which are disposed in axial symmetry with a rotational axis of the cam, and a plurality of guiding faces disposed in axial symmetry with a rotational axis of the cam and on a straight line perpendicular to a line passing through two second locking cam faces located axially opposite each other; and a shaft having a coupling portion for transmitting external torque; b) assembling the casing, the second gears, the cam and the cap with each other; c) aligning the coupling portion with the casing at a predetermined rotational angle; and d) press-fitting the shaft into a center hole of the cam.
An eighth aspect of the present invention is the method of manufacturing the reclining device according to the seventh aspect, wherein the step of aligning the coupling portion with the casing at a predetermined rotational angle is performed with the second gears engaged with the first gear at a predetermined rotational angle.
By disposing the reclining devices of this invention on both the right and left sides of the seat back and coupling them with each other, the seat back can be reliably and safely reclined to a predetermined angle. Further, since the rotational angle of the coupling portions of shaft with respect to the casing is the same on both sides, the connecting shaft can be easily coupled to each of the shafts. In other words, it becomes possible to minimize the play required for fitting the coupling portions in the connecting shaft. Further, it becomes possible to minimize the time difference of engagement or disengagement between the right and left sides when only one shaft is rotated. Therefore, the feeling when setting the angle of the seat back is improved.
Since minimal play is provided at the connection between the coupling portions of the shaft and the connecting shaft, even when a large force is transferred from a belt anchor to the seat cushion, and causes, for example, the shaft of the left side to rotate due to the elastic deformation of the seat cushion, and this rotation is then transmitted via the connecting shaft to the shaft of the right side, the tooth of the right side can be kept engaged with the first gear.